In ion-beam projection techniques for the production of semiconductors and semiconductive circuitry, it is known to provide an ion-beam projector which directs an ion beam along a beam axis onto the substrate wafer by providing along the path of this ion beam between the source and the substrate, an open-stencil mask whose openings define the structure which is transferred to the wafer. This technique, which is also referred to as shadow projection, locally blocks the beam in regions in which there are no openings in the mask. In a shadow projection, the image bears close to a 1:1 dimensional ratio with respect to the structure of the mask. Open-stencil masks, because of the techniques used in their manufacture, are frequently characterized by distortions in terms of positional shifts of the mask openings with respect to the desired positions thereof. These distortions are particularly disadvantageous when, as is common in the production of semiconductor circuits, a number of projections or imagings with different masks on the same substrate surface are required or desired.
In that case, the different masks may have different distortion states which can lead to intolerable shifts and contour inaccuracies in the imaged structures.
It is, therefore, desirable and even necessary in most cases to compensate for the distortions of each mask so that intolerable errors in the imaged structure do not arise.
The so-called "mix-and-match" process has been found to be particularly advantageous from an economic point of view. In this case the structuring of each semiconductor element is effected on two or more different apparatuses. For example, a coarse structuring can be effected by a low-cost optical wafer-stepper apparatus while the finer structuring is effected in an ion-projection apparatus.
In this case, the position of the image of the mask projected by the ion-beam projector on the wafer must be adjusted with great precision to the structures on the wafer already generated by the optical wafer-stepper apparatus.
Thus in both cases, i.e. in the case of distortion created by the ion-projection mask and in the case of the need for precise alignment of a subsequent ion-projection image with an earlier-form wafer-stepper image, a means for compensating the configuration and positions of the structures projected on the wafer is required.
There has already been described a process (H. Bohlen et al, Solid State Technology, September 1984, page 210) in which a narrow electron beam (diameter of about 1 mm) is displaced by a time-varying electrostatic deflection field in a raster pattern across the imaging mask in a so-called "scanning" process, whereby distortions which might be generated by the mask can be compensated by corresponding local changes in the deflection angle. This method has been found to be suitable only for scanning projection processes, since, at every point, the entire pencil of radiation is homogeneously deflected by the electrostatic field.